OBJECTIVE To determine the neural bases of visual deficits that occur during normal aging and to use the primate visual system for answering general questions about the effects of aging on the brain. RESULTS We are conducting an extensive survey of abilities in old (19 to 36 years) rhesus monkeys at the Wisconsin Regional Primate Research Center. The survey now includes data from >130 tests from 66 animals. The results to date indicate that old monkeys have significantly lower acuity than young adult animals. Acuity measured both at the level of the retina with the pattern electroretinogram (PERG) and at the cortical level with the visual evoked potential (VEP) is significantly lower in the old versus young adult monkeys. As predicted on the basis of human studies, there is also large overlap in the range of visual acuities at optimal refraction between old and young monkeys. We have also completed studies of the PERG and VEP to abrupt visual stimuli. Age-related differences were evident in the latency and waveform of the VEP, but not the PERG. In addition, there were gender differences in amplitude and latency that are strikingly similar to human VEP data. These results demonstra te that the rhesus monkey is an excellent model for the study of central-mediated visual loss during aging. In addition, we have demonstrated that propofol anesthesia does not affect PERG or VEP acuity measurements in young or old animals. We have made considerable progress this year with visual assessment using behavioral psychophysics. We have trained one young adult and one old animal to perform a two-alternative forced-choice task and have obtain complete contrast sensitivity data from these animals. Four additional animals are at an advanced stage of training. FUTURE DIRECTIONS We plan to conduct studies of the sensory properties of single neurons in the primate visual system and relate any functional or morphological changes to age-related deficits in visual abilities previously established with evoked potential and behavioral methods. These neurophysiological studies will use multi-unit recording methods to look for age-related changes in response properties and in interactions between cortical neurons. The behavioral and evoked potential survey data will be used to separate groups of animals with good and poor vision for further neurophysiological and anatomical study. KEY WORDS aging, vision, acuity, contrast sensitivity, evoked potentials FUNDING NIH AG11628